In the field of lighting technology, light emitting diodes, referred to with the abbreviation LED, are frequently used as a light source instead of the conventional halogen bulbs. LED light sources have also found a wide application in the lights of motor vehicles. However, LED light sources emit low-intensity light and therefore they are installed in higher quantities in a flat arrangement to increase the total luminous flux intensity. Among the lights of motor vehicles light guides occupy a special position as their elongated shape makes them especially suitable to create light lines positioned along the outline of headlights, or separately to create warning lights, e.g. positional, brake, indicator, or daily orientation lights. At present, light guides often fulfill signal light functions subject to higher requirements for the luminous flux, as e.g. the daily light in headlights and the rear brake and direction indication lights in the rear lamps. LED light sources are also used to supply light to the light guides of motor vehicles. They are located on the light guide face or they are installed in a recess of the entry part of the light guides. In principle, due to a small light guide diameter just one LED light source can only be used in one entry part of the light guide. The dimensions of most LED's in the market do not make it possible to use more than one diode in the entry part of the light guide. White LED's with miniature dimensions and a sufficient output for light guide applications are newly available in the market. The use of these miniature LED's enables a design in which two and more these LED's are fitted at one entry of a light guide. Using more than one LED at the light guide entry is only possible on condition the entry surface of the light guide is flat and no type of collimator can be used mainly to reduce the optical characteristics of the LED and to support subsequent propagation of light in the light guide. This design can only be used for power applications, as e.g. the daily lighting. For the time being, LED's are not available for the red light, i.e. sources necessary for light guide applications in rear group lamps for the “stop” function. The luminous flux in a light guide with a LED light source arranged on the light guide face may not be sufficient. Therefore, to increase the luminous flux the entry part of the light guide often has a parabolic shape that collimates light into the optical axis direction. However, the light guides have a small diameter and even a parabolic shape of the entry part does not guarantee a sufficient luminous flux, or efficient light distribution in the light guide.
The document U.S. Pat. No. 7,766,507 describes a shaped collimation lens with more elliptic surfaces for collimation of the luminous flux from the LED light source to the direction of the optical axis of the collimation lens. The side of the collimation lens facing the LED light source has a spherical recess in the center of which the LED light source is mounted. Thus, the rays emitted from the LED light source enter the collimation lens through the wall of the spherical recess without refraction. On its outer perimeter the collimation lens has the shape of the first ellipsoid whose first focus also lies in the center of the spherical recess where the LED light source is mounted. In its perimeter area, the side of the collimation lens, averted from the LED light source consists of a sector of the second ellipsoid lying inside the first ellipsoid and in the central area around the optical axis it consists of the vertex of the third ellipsoid oriented in the opposite direction against the first and second ellipsoid. The part of the rays that emitted from the LED light source in the perimeter area fall on the inner elliptic surface of the first ellipsoid and are refracted at a sharp angle to the optical axis and are collimated to the optical axis direction by passing through the elliptic area of the second ellipsoid. The part of the rays that emitted from the LED light source in the central area fall on the inner elliptic surface of the third ellipsoid and are refracted to the optical axis direction by passing through the inner elliptic surface of the third ellipsoid. To reinforce the luminous flux, the collimation lenses are arranged flatwise next to each other while the collimation lenses direct the rays of their LED light sources to the directions parallel to the optical axis of the light device. The collimation lenses according to the document U.S. Pat. No. 7,766,507 markedly collimate the light of the LED light source to the optical axis direction and therefore in a flat arrangement they are designed for area lighting and projection. Using individual collimation lenses for light guides of motor vehicles appears to be difficult especially due to their excessive size.
The aims of the invention are to eliminate the shortcomings of the prior art, increase the LED light source efficiency, improve concentration of the rays of the LED light source in the light guide, prevent losses of light from the light source in the light guide, achieve a better distribution and better homogeneity of the light beam propagating through the light guide. Another aim of the invention is to enable using of standard LED light sources to supply light guides designed for light functions and to achieve higher luminous fluxes.
Principle of the Invention
The aim of the invention is fulfilled by a light device consisting of a LED source and an elongated light guide, wherein the LED light source is seated in the entry part of the light guide for emitting the light beam into the light guide, wherein, according to the invention, the entry part of the light guide consists of mutually intersecting parts of at least two ellipsoids arranged with their main axes next to each other while the LED light sources are fitted in the first focuses of the ellipsoids for emission of light beams and their reflection from the elliptic walls of the ellipsoids to the second focuses of the ellipsoids lying inside the light guide in different distances from the first focuses of the ellipsoids. In other words, the distance between the second focus and the first focus in one of the ellipsoids is different than the distance between the second focus and the first focus in another of the ellipsoids. The ellipsoids can preferably have a rotational shape and their main axes can be arranged in parallel.
The distance of the second focus of the first ellipsoid from the first focus of the first ellipsoid can be preferably equal to at least 1.5 times the distance of the second focus of the second ellipsoid from the first focus of the second ellipsoid.
An advantage of the light device in accordance with the invention is higher efficiency of the LED light sources, better distribution and better homogeneity of the light beam propagating through the light guide. Another advantage is the possibility of using a suitable setting of the ratio of the focal distances of the elliptic entry parts to optimize the distribution of the light beam inside the light guide.